Controlled thermal coating

ABSTRACT

The combined measurement of particle speed, particle temperature, particle intensity, burner current and the control thereof within a tolerance range allow the coating structure, coating thickness and the coating weight to be maintained despite wear-associated fluctuations in the coating process.

The invention relates to a thermal coating process. Thermal spraying processes are used for producing metallic and ceramic layers, in which a material melts completely or at least partially.

The material is injected into a nozzle, for example of a plasma torch, or externally. The nozzle, at least, becomes worn owing to very high plasma temperatures and the inflow of powder material. This leads to wear-related fluctuations in the coating process, which are caused primarily by a drop in voltage at the torch.

To date, these fluctuations have been compensated for by readjusting the powder mass flow, in order to keep the desired layer weight of the blade or vane in the tolerance range.

This is not optimal, however, since merely the drop in power at the torch which is induced by the drop in voltage is compensated for by an increase in the powder mass flow.

It is an object of the invention, therefore, to solve the aforementioned problem.

The object is achieved by a method as claimed in claim 1.

The dependent claims list further advantageous measures which can be combined with one another, as desired, in order to obtain further advantages.

In the drawings:

FIGS. 1-3 show parameter profiles from the prior art,

FIGS. 4-9 show parameter profiles according to the invention,

FIG. 10 shows a nozzle,

FIGS. 11, 12 show a temperature distribution,

FIG. 13 shows a turbine blade or vane.

The description and the figures represent only exemplary embodiments of the invention.

Coatings are applied by thermal coating processes such as SPPS, HVOF, APS, LPPS, VPS, . . . . In these processes, a plasma or a flame is generated in a nozzle, a material flowing in through the nozzle or at the end of the nozzle.

The wear on the nozzle or on the coating apparatus causes the material flow properties and therefore also the degree of melting of the material, in particular of the powder, to change.

FIG. 1 shows an exemplary profile of the voltage U_(B) between the nozzle 30 and an electrode 36 (FIG. 10) according to the prior art.

The voltage U_(B) between the nozzle 30 and the electrode drops over time t and then merges into saturation. In the case of other types of nozzle, a continuous drop in the voltage U_(B) over time t or other profiles are also possible.

The profile of the average temperatures T and of the average material flow velocity v_(P) (not shown) over time is analogous.

As an effect of this, the layer weight m_(c) decreases over time (FIG. 2) and/or the porosity p (FIG. 3) increases.

The properties of the flame or of the plasma and/or of the molten material, which emerge from the nozzle 30 during the thermal coating, in particular during the plasma coating or HVOF coating, are therefore determined according to the invention.

In this respect, what are determined are target values Z1, Z2, Z3, such as in particular of the voltage U_(B) between the nozzle and the electrode 36 or the power P at the nozzle 30, material flow velocity v_(P), the temperature T_(P) of the material flow 42 and/or a brightness distribution H(x,y) or temperature distribution T(x,y), where H=light intensity or radiation power of the particles Mxy in the material flow 42. This is effected by measuring instruments, which determine quantitative data by way of pyrometry or CCD cameras.

If deviations are thus identified during the measurement, it can be concluded that wear has occurred, and parameters R1, R2, R3 for varying the target variables Z1, Z2, Z3 are accordingly set, such that the desired target values of Z1, Z2, Z3 are achieved again.

The target values (Z1, Z2, Z3) are controlled through the adaptation of the control variables (R1, R2, R3), here the current intensity I_(B) of the nozzle 30, and the flow rates of the primary and/or secondary gases in H₂, in A_(r) at the nozzle 30, by virtue of which the target parameters Z1, Z2, Z3 can be set in a targeted manner.

Primary gases are argon (Ar) and/or helium (He) and secondary gas is, for example, hydrogen (H₂), these flowing through the nozzle 30.

Use may be made of one, two or three control variables, proceeding from an optimum desired state for Z1, Z2, Z3 for the three control variables R1, R2, R3 used here.

Proceeding from the control variables R1, R2, R3, with which the target variables Z1, Z2, Z3 are observed, parameter sets K1, K2, . . . , with which the control variables R1, R2, R3 are simultaneously or partially increased (>1.0) or reduced (<1.0) or remain constant (1.0), are determined beforehand.

Here, 1.0 represents a nominated value for R1, R2, R3, . . . , that is the set value divided by the initial state of R1, R2,

The values 1.1; 0.9 correspondingly represent a corresponding increase or reduction of R1, R2, . . .

R1 R2 R3 K1 1.1 1.1 1.1 K2 1.1 1.0 1.0 K3 1.1 1.0 1.1 K4 1.1 1.0 0.9 K5 0.9 0.9 0.9 K6 0.9 1.1 1.0 K7 . . . . . . . . .

On account of these increases and/or variations in the control variables R1, R2, R3, the varied values of the, preferably three, target variables Z₁, Z₂, Z₃ used here are then determined:

R1 R2 R3 Z1 Z2 Z3 K1 1.1 1.1 1.1 1.2 0.8 0.8 K2 1.1 1.0 1.0 1.2 1.2 1.2 K3 1.1 1.0 1.1 1.2 1.2 1.2 K4 1.1 1.0 0.9 1.2 1.2 1.2 K5 . . . . . . . . . . . . . . . . . .

The values 1.1; 0.9; 1.0 correspondingly represent a corresponding increase, reduction or no variation in the standardized values of Z1, Z2, . . .

The variations in the target variables Z1, Z2, Z3, here the particle temperature T_(P), voltage U_(B), power P and particle velocity, depend on the respective nozzle 30.

It is similarly possible to record a data table only with higher (↑) and lower (↓) values for R1, R2, . . . , i.e. no constant values (-) for the control variables.

R1 R2 R3 Z1 Z2 Z3 K1 1.1 1.1 1.1 1.2 0.8 0.8 K8 1.1 1.1 0.8 1.2 1.2 1.3 K9 1.1 0.9 1.1 1.2 1.1 1.1 K10 0.9 1.1 0.9 1.2 1.2 1.2 K11 • • • • • •

It is similarly possible to formulate the higher (1.0) or lower (0.9) values of R1, R2, R3 with different magnitudes and to determine the effect on the target variables Z1, Z2, Z3:

K1: R2 has greater variations on a percentage basis than R1, R3; K2: R1 has greater variations on a percentage basis than R2, R3; K4: R3 smaller than R1, R2.

R1 R2 R3 Z1 Z2 Z3 K12 1.1 1.2 1.1 1.1 0.9 0.9 K13 1.2 1.1 1.1 1.1 1.4 1.2 K14 1.1 1.1 1.1 1.1 1.1 1.1 K15 1.1 1.0 0.8 1.1 1.1 1.1

These parameter sets K1, . . . determined in advance are then used for control if a deviation occurs for Z1, Z2, Z3.

If the value deviates from Z1, Z2, . . . , it is determined which combination K1, K2, . . . of Z1, Z2, Z3 comes closest to the deviation, if appropriate a best-fit adaptation is carried out, and the control values R1, R2, R3 of this combination K1, K2, . . . thus found are then used for the further operation of the nozzle 30 and electrode 36, in order to compensate for the deviations.

As a result of this control, the layer structure, the layer thickness and the layer weight m_(c) (FIG. 6) of the blade or vane and also the porosity p (FIG. 7) remain constant over time t.

As a result of the current intensity I_(B) being controlled (FIG. 4), the power P is kept relatively constant (FIG. 5). This is then also identifiable from the constant values of the particle temperatures and the particle velocities V_(P) (not shown).

FIG. 10 shows a nozzle 30, in which argon (Ar) or helium (He) are introduced as primary gas and/or hydrogen (H₂) is introduced as secondary gas at one nozzle end 31, and at the other end 33 material (Mx,y) is added.

By virtue of the application of the voltage U_(B) between the electrode 36 and the nozzle 30, a high-energy arc generates a plasma, which forms the plasma flame.

Similarly, it is possible for the gas flow rates {dot over (m)}_(G) of argon {dot over (m)}_(Ar) (FIG. 8) and also those of hydrogen {dot over (m)}_(H2) (FIG. 9) at the nozzle 30 to be controlled, in order to achieve the desired results, in particular for the voltage U_(B).

FIG. 11 shows a distribution 36 of the temperature T(x,y) or of the brightness H(x,y) in the outflow direction z of the material flow 42.

Here, there is a hottest, inner core 39′ and regions 39″, 39′″ which are located further outward and are less hot. The presence of a plurality of regions 39′, 39″, 39′″ is only schematic here in respect of a continuous drop or variation in the temperature or brightness.

FIG. 12 is a lateral view of the material flow 42 and the brightness distribution H(x,y) thereof or the temperature distribution T(x,y) thereof.

In this lateral view, the brightness values in the x direction are added up for a y position.

The brightness H(x,y) is determined by all particles M_(xy) along the x direction for a position y and the temperature T of the particles M_(xy), since not only do the outer particles radiate in the region 39′″, but also the inner particles radiate outward in the region 39′ and are sensed.

The temperature T(x,y) is instead determined only by the outer particles in the region 39′″.

It is also possible for an integral value R of an area ∫H(x,y)dxdy to be determined over the plan view shown in FIG. 11 or FIG. 12, and an individual integral brightness value R is formed.

This value R can be used for control.

If deviations are identified in this integral value R, control occurs.

It is similarly possible for an integral temperature value R=∫′T(x,y)dxdy to be determined over the cross section shown in FIG. 12 or FIG. 11 for the control.

This integral, singular value R then also represents a control variable Z.

Similarly, it is possible for a visual comparison to be made at various times between two images of FIGS. 11 and 12 for the temperature distribution T(x,y) or brightness distribution H(x,y), and for deviations to be determined.

If deviations are identified, control likewise occurs.

The material flow rate {dot over (m)}_(M) of the material flow is in this case preferably not varied during the control.

FIG. 13 shows a perspective view of a rotor blade 120 or guide vane 130 of a turbomachine, which extends along a longitudinal axis 121.

The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor.

The blade or vane 120, 130 has, in succession along the longitudinal axis 121, a securing region 400, an adjoining blade or vane platform 403 and a main blade or vane part 406 and a blade or vane tip 415.

As a guide vane 130, the vane 130 may have a further platform (not shown) at its vane tip 415.

A blade or vane root 183, which is used to secure the rotor blades 120, 130 to a shaft or a disk (not shown), is formed in the securing region 400.

The blade or vane root 183 is designed, for example, in hammerhead form. Other configurations, such as a fir-tree or dovetail root, are possible.

The blade or vane 120, 130 has a leading edge 409 and a trailing edge 412 for a medium which flows past the main blade or vane part 406.

In the case of conventional blades or vanes 120, 130, by way of example solid metallic materials, in particular superalloys, are used in all regions 400, 403, 406 of the blade or vane 120, 130.

Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949.

The blade or vane 120, 130 may in this case be produced by a casting process, by means of directional solidification, by a forging process, by a milling process or combinations thereof.

Workpieces with a single-crystal structure or structures are used as components for machines which, in operation, are exposed to high mechanical, thermal and/or chemical stresses. Single-crystal workpieces of this type are produced, for example, by directional solidification from the melt. This involves casting processes in which the liquid metallic alloy solidifies to form the single-crystal structure, i.e. the single-crystal workpiece, or solidifies directionally. In this case, dendritic crystals are oriented along the direction of heat flow and form either a columnar crystalline grain structure (i.e. grains which run over the entire length of the workpiece and are referred to here, in accordance with the language customarily used, as directionally solidified) or a single-crystal structure, i.e. the entire workpiece consists of one single crystal. In these processes, a transition to globular (polycrystalline) solidification needs to be avoided, since non-directional growth inevitably forms transverse and longitudinal grain boundaries, which negate the favorable properties of the directionally solidified or single-crystal component.

Where the text refers in general terms to directionally solidified microstructures, this is to be understood as meaning both single crystals, which do not have any grain boundaries or at most have small-angle grain boundaries, and columnar crystal structures, which do have grain boundaries running in the longitudinal direction but do not have any transverse grain boundaries. This second form of crystalline structures is also described as directionally solidified microstructures (directionally solidified structures).

Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1.

The blades or vanes 120, 130 may likewise have coatings protecting against corrosion or oxidation, e.g. (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon and/or at least one rare earth element, or hafnium (Hf)). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1.

The density is preferably 95% of the theoretical density. A protective aluminum oxide layer (TGO=thermally grown oxide layer) is formed on the MCrAlX layer (as an intermediate layer or as the outermost layer).

The layer preferably has a composition Co-30Ni-28Cr-8Al-0.6Y-0.7Si or Co-28Ni-24Cr-10Al-0.6Y. In addition to these cobalt-based protective coatings, it is also preferable to use nickel-based protective layers, such as Ni-10Cr-12Al-0.6Y-3Re or Ni-12Co-21Cr-11Al-0.4Y-2Re or Ni-25Co-17Cr-10Al-0.4Y-1.5Re.

It is also possible for a thermal barrier coating, which is preferably the outermost layer and consists for example of ZrO₂, Y₂O₃—ZrO₂, i.e. unstabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, to be present on the MCrAlX.

The thermal barrier coating covers the entire MCrAlX layer. Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD).

Other coating processes are possible, e.g. atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may include grains that are porous or have micro-cracks or macro-cracks, in order to improve the resistance to thermal shocks. The thermal barrier coating is therefore preferably more porous than the MCrAlX layer.

Refurbishment means that, after they have been used, protective layers may have to be removed from components 120, 130 (e.g. by sand-blasting). Then, the corrosion and/or oxidation layers and products are removed. If appropriate, cracks in the component 120, 130 are also repaired. This is followed by recoating of the component 120, 130, after which the component 120, 130 can be reused.

The blade 120, 130 may be hollow or solid in form. If the blade 120, 130 is to be cooled, it is hollow and may also have film-cooling holes 418 (indicated by dashed lines). 

1. A method for thermal coating by means of a material flow (42) by means of a nozzle (30), in particular by means of a powder flow, in which a material (M_(xy)) of the material flow (42) is heated, partially melted and/or melted, in particular by means of a plasma or a flame, in which at least one of the target variables (Z₁, Z₂, Z₃, . . . ) material flow velocity (v_(P)) of the material flow (42) and/or brightness distributions (H(x,y); ∫H(x y)dxdy) or temperature distribution (T(x,y); ∫T(x,y)dxdy) of the material flow (42) and/or voltage (U_(B)) between an electrode (36) and the nozzle (30) and/or the power (P) of the nozzle (30) are measured or determined and controlled.
 2. The method as claimed in claim 1, in which a brightness distribution (H(x,y);) ∫H(x,y)dxdy) of the material flow (42) or the voltage (U_(B)) between the nozzle (30) and the electrode (36) or the power (P) at the nozzle (30) are controlled as at least one target variable (Z₁, Z₂, Z₃, . . . ).
 3. The method as claimed in claim 1, in which, as target variables (Z₁, Zd₂), either the material flow velocity (v_(P)) and the voltage (U_(B)) between the nozzle (30) and the electrode (36) or the material flow velocity (v_(P)) and the power (P) at the nozzle (30) are controlled.
 4. The method as claimed in claim 1, in which, as target variables (Z₁, Z₂), a brightness distribution (H(x,y); ∫H(x y)dxdy) of the material flow (42) and the material flow velocity (v_(P)) are controlled.
 5. The method as claimed in claim 1, in which, as target variables (Z₁, Z₂), a temperature distribution (T(x,y); ∫′T(x,y)dxdy) of the material flow (42) and the material flow velocity (v_(P)) are controlled.
 6. The method as claimed in claim 1, in which, as target variables (Z₁, Z₂, Z₃), either a temperature distribution (T(x,y); ∫T(x,y)dxdy) of the material flow (42), the material flow velocity (v_(P)) and the voltage (U_(B)) between the nozzle (30) and the electrode (36) or a temperature distribution (T(x,y); ∫T(x,y)dxdy) of the material flow (42), the material flow velocity (v_(P)) and the power of the nozzle (30) are controlled.
 7. The method as claimed in claim 1, in which, as target variables (Z₁, Z₂, Z₃), either the brightness distribution (H(x,y); ∫H(x,y)dxdy) of the material flow (42), the material flow velocity (v_(P)) and the voltage (U_(B)) between the nozzle (30) and the electrode (36) or the brightness distribution (H(x,y); ∫H(x,y)dxdy) of the material flow (42), the material flow velocity (v_(P)) and the power (P) at the nozzle (30) are controlled.
 8. The method as claimed in one or more of claim 1, 2, 3, 4, 5, 6 or 7, in which the current intensity (I_(B)) between the nozzle (30) and the electrode (36) and/or the gas flow rates ({dot over (m)}_(H2), {dot over (m)}_(Ar)) of the nozzle (30) are varied as control variables (R1, R2, R3), in order to keep the target variables (Z1, Z2, Z3) such as the brightness distribution (H(x,y); ∫H(x,y)dxdy) of the material flow (42) or the temperature distribution (T(x,y); ∫T(x,y)dxdy, of the material flow (42) or the voltage (U_(B)) at the nozzle (30) or the power (P) at the nozzle (30) and/or the material flow velocity (v_(P)) in a specific tolerance range or constant.
 9. The method as claimed in one or more of claims 1 to 8, in which the current intensity (I_(B)) is increased or lowered as a control variable (R1, R2, R3).
 10. The method as claimed in one or more of claims 1 to 9, in which the gas flow rate ({dot over (m)}_(Ar), {dot over (m)}_(H2)) of the primary gases (argon, helium) and/or of the secondary gases (hydrogen, . . . ) of the nozzle (30) are increased or lowered as at least one control variable (R1, R2, R3).
 11. The method as claimed in one or more of claims 1 to 10, in which the material flow rate ({dot over (m)}_(m)) is not varied during the coating.
 12. The method as claimed in one or more of claims 1 to 11, in which the temperature distribution (T(x,y)) of the material flow (42) is used as the temperature.
 13. The method as claimed in one or more of claims 1 to 11, in which an integral value (∫T(x,y)dxdy) of the material flow (42) is used as the temperature of the material flow (42).
 14. The method as claimed in one or more of claims 1 to 11, in which an integral value (∫H(x,y)dxdy) of the material flow (42) is used as the brightness value.
 15. The method as claimed in one or more of claims 1 to 11, in which the brightness distribution (∫H(x,y)dxdy) of the material flow (42) is used as the brightness value.
 16. The method as claimed in one or more of claim 1 to 11, 14 or 15, in which the light intensity or radiation power of the material flow (42) is used as the brightness value (H).
 17. The method as claimed in one or more of claims 1 to 16, in which an HVOF method is used.
 18. The method as claimed in one or more of claims 1 to 16, in which a plasma spraying method is used.
 19. The method as claimed in one or more of claims 1 to 18, in which, before the coating, proceeding from one and/or more initial values of the control variables (R1, R2, R3) at which the desired target variables (Z1, Z2, Z3) are achieved and/or maintained, sets of parameters for various constellations, such as higher, lower and constant, of the control variables (R1, R2, R3) are set, and the variations in the target variables (Z1, Z2, Z3) are determined, these then being used later for control. 